A display apparatus that includes an erecting unit magnification optical system having a two-dimensional array of microlenses is described in, for example, Patent Document 1. In this display apparatus, a liquid crystal display is arranged at one side of the erecting unit magnification optical system. The erecting unit magnification optical system forms an erecting unit magnification stereoimage of an image displayed on the liquid crystal display at the opposite side of the liquid crystal display. In this stereoimage display apparatus, the erecting unit magnification stereoimage is emphasized on a blurred background image generated by a perforated color plate. When an observer looks at the erecting unit magnification stereoimage with both eyes, a floating image can be seen.
A conventional erecting unit magnification optical system used in a scanner or a copier is described in, for example, Patent Document 2. As shown in FIG. 1, the erecting unit magnification optical system includes two lens array plates 103. Each of the lens array plates 103 has a plurality of microlenses 103a that are arranged in such a manner that their optical axes are parallel to one another. The optical axes of the microlenses 103a of one lens array plate 103 are aligned with the optical axes of the microlenses 103a of the other lens array plate 103. The peaks of the microlenses 103a of one lens array plate 103 come in contact with the peaks of the microlenses 103a of the other lens array plate 103. In the erecting unit magnification optical system, a high-resolution image is produced when the spherical aberration of each microlens 103a is reduced.
To produce a high-resolution image, each microlens of the conventional erecting unit magnification optical system has a small spherical aberration. Thus, even a slight change in the distance between an object 15 (image shown on a liquid crystal screen) and the microlenses 103a would greatly blur the image 15a. Thus, the positional relationship between the conventional erecting unit magnification optical system and the object 15 cannot be changed.
The display apparatus described in Patent Document 1 is disadvantageous in that moire may be generated. Moire is a phenomenon in which a pattern of regular stripes is generated by the interference between the microlenses and the pixels of the liquid crystal display. Moire lowers the image quality.
An apparatus for displaying a three-dimensional image with suppressed moire is described in, for example, Non-Patent Document 1. This conventional apparatus displays a stereoimage on a lenticular sheet on which a plurality of cylindrical lenses are arranged. The cylindrical lenses on the lenticular sheet increase the resolution in units of sub-pixels and not in units of pixels. Each cylindrical lens emits monochromatic light of one of RGB. This structure suppresses color moire. However, it is difficult to manufacture a cylindrical lens having dimensions that are smaller than a pixel. In particular, it is extremely difficult to manufacture a mold for the above lenticular sheet.
An apparatus for displaying a stereoimage with suppressed moire is described in, for example, Patent Document 3. This three-dimensional image display apparatus includes a planar display and a screen. The planar display has a plurality of pixels, each of which includes three sub-pixels. The screen divides the image into disparity images by limiting the travel direction of light emitted from each sub-pixel. The disparity images are viewed by the observer as a three-dimensional image. To suppress moire, the screen includes screen elements that are arranged at an interval obtained from the sum of an integral multiple number of the pixel pitch and an integral multiple number of the sub-pixel pitch. With this structure, moire would become too narrow to be recognized. However, this structure suppresses moire only when the planar display is spaced by a predetermined distance from the screen. This structure does not permit the distance between the planar display and the screen to be changed.
Examples of other display apparatuses for displaying stereoimages are described in Patent Documents 4 and 5. However, the positions of images displayed by the apparatuses of Patent Documents 4 and 5 are fixed and cannot be changed.
Patent Document 1: Japanese Patent No. 3195249
Patent Document 2: Japanese Laid-Open Patent Publication No. 64-88502
Patent Document 3: Japanese Laid-Open Patent Publication No. 2004-118414.
Patent Document 4: Japanese Laid-Open Patent Publication No. 07-144578
Patent Document 5: Japanese Laid-Open Patent Publication No. 2004-334590
Non-Patent Document 1: R. Börner, “Displays 20 (1999)”